1. Field of the Invention
The present invention relates generally to a fiber having a multi-ply laminar structure and to a structure employing the same, particularly to a color-developing composite short fiber which reflects visible or invisible rays and interferes with them to develop a color with high transparency and has sophisticated design and which also has excellent optical properties, and also to a color-developing structure formed by adhering the fiber on a support such as a sheet, a film or a metal plate or to a color-developing structure having the form of sheet, nonwoven fabric, paper or the like formed by binding such fibers.
2. Description of the Related Art
Recently, fibers having expressiveness such as bulkiness are being developed by using fibers with modified cross sections instead of simple round cross sections and by combining two or more kinds of fibers so as to satisfy demands for high-quality textures in fabrics, and they made entries as new fibers into the market. Fibers having more sophisticated expressiveness or functions are now in demand, and what are required of the fibers include color deepness and luster. However, if a fiber having a deep color and luster is to be obtained, an unvivid dull-colored fiber is resulted, although it may have a deep color; whereas if one tries to obtain a lustrous fiber, a gaudy glittery fiber is resulted. Accordingly, there has so far developed no technique for producing fibers fully satisfying both color depth and luster, as far as the present inventors know.
The reason is that dyes and pigments have been employed for developing colors in the prior art, and since dyes and pigments develop colors based on light absorption, the deeper is the color one tries to obtain, the smaller becomes the reflected light to cause the luster to be lost. Now, when we look around the natural world, we will find creatures satisfying both color depth and luster, for example, jewel beetles and morpho butterflies, and they have colors satisfying color depth and luster simultaneously. These creatures develop colors respectively resorting to reflection and interference of light as the mechanism of color development, and extensive studies are being made so as to find out whether this dolor-developing mechanism can be utilized in synthetic fibers.
For example, Japanese Patent Publication No. Sho 43-14185 discloses a coated three-layer composite fiber having pearl effect. It is true, however, such fibers having merely three layers may develop colors based on light reflection and interference, but the degree of color development is too limited to be able to satisfy the demands for higher expressiveness. Meanwhile, as described in Japanese Patent Publication No. Sho 60-1048, a multilayered synthetic fiber whose interfaces are all substantially parallel to one another can be obtained by combining different kinds of polymers alternately and repeatedly in a spinning pack equipped with a stationary mixer, and the resulting polymer is injected through injection orifices. In this official gazette, there is described an example of composite fiber consisting of polyethylene terephthalate and nylon 6 formed by layering them via a multilayered film component employing a stationery mixer, and this fiber can give textiles having pearl effect.
However, if a multilayered fiber is to be obtained according to this method, the laminar flow is disturbed little by little each time two polymers are combined with each other. Although a multilayered structure can be obtained somehow, this technique is not satisfactory to obtain a multilayered structure having a thickness controlled with optical accuracy. Particularly, when a multilayered structure having 10 or more layers is to be formed, polymers must be combined several times or more, so that the layers are liable to have irregular thickness giving coherent beams of light having insufficient intensity and that coherent beams of light having various wavelengths, that is to say, turbidity in color, are observed, resulting in the failure of obtaining a color having satisfactory expressiveness.
Further, Japanese Patent Publication No. Sho 57-20842 describes a static fluid mixer; and Japanese Patent Publication Nos. Sho 53-8806 and Sho 53-8807 describe methods of spinning blended yarns and apparatuses therefor. According to these methods, fibers are obtained by combining two kinds of polymers and separating them repeatedly, so that the polymers are mixed due to complication of the polymer flows to be unsuccessful in forming a multilayered structure having optical dimensions. Japanese Unexamined Patent Publication Nos. Sho 62-170510 also discloses a method for obtaining coherent beams of light by forming fine unevenness on the fiber surface. According to this method, interference of light is induced by forming a diffraction grating on the fiber. A like method is disclosed in Japanese Unexamined Patent Publication No. Hei 4-202805. In these methods, although such fibers may show color development based on interference of light, the wavelength of coherent beams of light in fabrics woven by them vary depending on the angle of view like in the thin film as described above. That is, in this case, the colors of the fabrics vary only to give cheap and unsatisfactory expressiveness.
In addition, Japanese Unexamined Patent Publication Nos. Sho 59-228042 and Sho 63-64535, Japanese Patent Publication No. Sho 60-24847, etc. propose color developing fibers and fabrics developed taking a hint from the morpho butterflies in South America which are famous for their variable color tone depending on the angle of view and bright color effect. However, the fibers employed in the inventions described in the above official gazettes are flat yarns formed by laminating different kinds of polymers together, so that it is almost impossible to obtain a thickness so as to induce interference of light even if these polymers are laminated, and such structures merely serve to control reflection of light. Meanwhile, another proposal is described in Japanese Unexamined Patent Publication No. Sho 54-42421 disclosing a method for obtaining a multi-ply lamination fiber of different kinds of polymers is disclosed. However, in this method, the laminated portion is allowed to assume a hollow annular form, and one component in the laminated portion is melted to obtain a superfine fiber. Accordingly, this proposal does not suggest such fibers as can give the effect of interference in which multiple layers are all allowed to have optical dimensions.
There is also published a technique for obtaining a material which shows color development by employing a sandwich structure of a molecule-oriented anisotropic film between a pair of polarizing films (e.g., Journal of Textile Machinery Society, Vol. 42, No. 2, p.55 (1989), and Vol. 42, No. 10, p.160 (1989), ibid.). Further, Japanese Unexamined Patent Publication Nos. Hei 7-97766 and Hei 7-97786 disclose fiber fabrics each having on the surface a light interference film provided with a substantially transparent thin film layer which can develop color with the aid of the reflected light of incident light from the front surface and the light reflected by the rear surface. Wavelength of coherent beams of light resorting to such thin films varies depending on the angle of view, so that the color of the fabric changes depending on the angle of view, only to give here again cheap expressiveness.
Under such circumstances, the present inventors was successful in enabling formation of a multilayered structure having a ply number of more than 10 so as to obtain a single color development and also in developing a composite polymer fiber which has a uniform ply thickness and a thin-layer laminar portion formed by laminating alternately two kinds of polymers which develop effective interference color, a technique for forming it and a spinneret employable for forming it, and they recently filed a patent application.
However, when a color-developing composite fiber obtained according to this technique is woven into plain weave fabric or used as stitch yarns, it is difficult to obviate torsion of the yarns and to orient accurately all of the faces exhibiting optical properties to face forward on an article. This torsion inevitably brings about reduction in chromaticity, i.e. reduction in the ability of developing the desired color which is the optical property characteristic to color-developing composite fibers. Meanwhile, the smaller is the compression rate of the cross section, the higher becomes the liability of occurrence of torsion. Further, even when the faces exhibiting optical properties are oriented accurately to face forward, their excellent optical properties can be reduced or impaired slightly if the fiber particles are overlapping one another. In other words, the chromaticity of high reflectance and high transparency can be slightly impaired.
The present invention relates to a composite fiber which maintains high reflectance and develops a color with high transparency and excellent designability, as well as, to various forms of color-developing structures (coat, resin tapes, nonwoven fabrics, etc.) utilizing the composite fiber.
Means employed for achieving the above objectives in the present invention can be divided into the following two:
The first means is a color-developing composite short fiber composed of two or more polymer compounds having different refractive indices laminated alternately which reflects visible rays and interferes with them and has a length of 0.01 to 100 mm, or a color developing structure formed by binding the fiber particles to one another, or by dispersing fiber particles in or mixing them with other materials to be bound therewith, or by adhering the fiber particles on the surface of a support. Since visible rays make colors to be perceptible to human eyes, the structures of the present invention can realize a deep and lustrous color resorting to reflection and interference of visible rays, providing excellent chromaticity.
Meanwhile, the second means is a color-developing composite short fiber, which is formed by laminating alternately two or more kinds of polymer compounds having different refractive indices, is composed of a layer which reflects visible rays and interferes therewith and a layer which reflects invisible rays and interferes therewith and has a length of 0.01 to 100 mm, and a color developing structure formed by binding the fiber particles to one another, or by dispersing fiber particles in or mixing them with other materials to be bound therewith, or by adhering the fiber particles on the surface of a support. Infrared rays are heat rays, and since reflection and interference of infrared rays mean interruption of heat rays, fiber products employing such fibers have the effect of inhibiting increase of temperatures in substances and human bodies. While ultraviolet rays are harmful to human bodies, fiber products employing the fibers of the present invention have the effect of controlling malicious influence of such rays.
These constitutions of the present invention are based on findings obtained as the result of research and development made by the present inventors so as to make better use of the characteristics of the fibers developed by them. In other words, short-cut particles of color-developing composite fiber can be distributed without causing torsion, if they are dispersed on a plate-like body. Particularly when the short-cut particles have flat cross-sections, faces exhibiting optical properties can be orientated to face forward in most particles. If the short-cut fiber particles are dispersed a little more carefully, they can also be dispersed not to overlap much. Accordingly, the problems inherent in the prior art can be solved according to such a simple technique, and effects specific to composite fibers having the optical properties as described above can fully be exhibited.
Meanwhile, in the case of non-cut long fibers, since changes in the orientation directions of the faces exhibiting optical properties is attributed to torsion, such changes occur gradually. However, in the case of short fibers which are masses of short fiber particles, the orientation directions of the fiber particles do not depend on one another, orientation directions of the faces exhibiting optical properties of adjacent fiber particles can be changed abruptly. Accordingly, in this respect, it was found that there are differences between the long fibers and short fibers in their optical properties.
As described above, short fibers can be utilized in the forms which cannot be realized by long fibers, even if they are of the same color developing fiber materials, and various forms of structures, which cannot be expected to be realized using long fibers, for example, nonwoven fabrics, paper, etc. can be formed.
Now, the color-developing composite short fiber to be provided according to the present invention will be described below in terms of its structure, production technique, characteristics, etc.
FIG. 1 shows a cross section of a color-developing composite fiber taken perpendicular to the long axis of the fiber, and the cross-sectional configuration as shown in FIG. 1 is necessary so that the fiber may exhibit the desired characteristics of reflecting and refracting visible or invisible rays according to the present invention. The fiber shown in FIG. 1(a) is of the structure in which two kinds of polymer compound materials having different refractive indices are merely laminated alternately; while the fiber shown in FIG. 1(b) is of the structure in which the laminated structure as shown in FIG. 1 is covered with one of the polymer compound materials; and the fiber shown in FIG. 1(c) is of the laminar structure having two kinds of ply thicknesses so as to effect reflection and interference of two kinds of rays, i.e. visible rays and invisible rays such as infrared rays. Fibers having such cross-sectional configurations are to be all included in the composite fibers to be employable for forming short fibers according to the present invention.
In order to allow these composite fibers to have actions of reflecting visible rays and interfering therewith to develop color, the cross-sectional configurations of the fibers are required to satisfy the following requirements: In the laminated portion of a fiber structure, when the optical refractive index and thickness of a high-refractive index material are na and da, and those of a low-refractive index material are nb and db, respectively, na, da, nb and db shall satisfy the following relationship: 0.38 xcexcmxe2x89xa6xcex1xe2x89xa60.78 xcexcm wherein xcex1=2(nada+nbdb), with the proviso that 1.0xe2x89xa6na xe2x89xa61.8, 1.3xe2x89xa6nbxe2x89xa61.8 xcexcm and 1.01xe2x89xa6nb/naxe2x89xa61.8.
Here, xcex1 means peak wavelengths (xcexcm) in a reflection spectrum, and in this case the primary peak wavelength. In these expressions, nada and nbdb show xe2x80x9cthe product of optical refractive index and thicknessxe2x80x9d of the high-refractive index material and that of the low-refractive index material respectively. xe2x80x9cThe product of optical refractive index and thicknessxe2x80x9d is generally referred to as xe2x80x9coptical thicknessxe2x80x9d. Accordingly, the sum of the optical thickness of the high-refractive index material and that of the low-refractive index material multiplied by 2 give the desired peak wavelength xcexc1.
Meanwhile, in order to allow a layer to have actions of reflecting invisible rays such as infrared rays other than visible rays, infrared reflection and interference layer and ultraviolet reflection and interference layer should satisfy the requirements 0.78 xcexcmxe2x89xa6xcex1xe2x89xa62 xcexcm and 0.2 xcexcmxe2x89xa6xcex1xe2x89xa60.38 xcexcm, respectively, under the above conditions.
Under the above conditions, the thicknesses of the layers are: infrared reflecting layer greater than visible ray reflecting layer greater than ultraviolet reflecting layer. Incidentally, the ply numbers N of these three layers having optical functions of reflecting visible rays, infrared rays and ultraviolet rays respectively depend on which function is selected primarily. For example, in the case where the color developing function is selected as the primary function and the other functions as secondary functions, the ply number N of the visible ray reflecting layer is increased compared with those of the reflecting layers having other functions, and thus not only the reflectance at the peak wavelength xcexc1 can be increased, but also the function of the layer can be improved.
Referring to the arrangement of the visible ray reflecting layer and two other invisible ray reflecting layers, in terms of the layered cross section, it may not particularly be limited, and any of these three layers may be located on the inner side. For example, when an infrared reflecting layer and an invisible ray reflecting layer are to be laminated, the thin invisible ray reflecting layer may be located on the inner side, or it may be arranged on the outer side and the infrared ray reflecting layer may be located on the inner side. Further, this fiber preferably has a cover so as to be surrounded entirely on the surface, as shown in FIG. 1(b). Thus, an improved fiber structure can be obtained, since the layered side faces are prevented from being exposed directly, as shown in FIG. 1(a), and ply separation between lamination planes can be prevented from occurring at the lamination interfaces, and abrasion resistance of the fiber can also be improved. If a material having a low melting point is used for forming the cover, it can be utilized for fusing the fiber particles on the surface of a support or fusing them with one another.
Further, referring to the cross-sectional configuration of the fiber, it is preferably of flat profile such that the faces exhibiting optical properties have larger surface area and the faces orthogonal thereto have smaller surface area. Thus, the face exhibiting optical properties can accurately be orientated to face forward and to develop a uniform color having high reflectance and transparency. However, the present invention is not to be limited to such configurations, and various kinds of cross-sectional configurations such as a square overall configuration can be employed. When a cross-sectional configuration having a low compression ratio is employed, faces other than those exhibiting optical properties are very likely to be oriented to face forward, and although it is inevitable that the fiber comes to have a high reflectance and that its transparent color is lightened, there occurs no reduction in the chromaticity as will be induced by torsion in long fibers. On the contrary, orientation directions of the faces exhibiting optical properties can rather be changed even between adjacent fiber particles, and thus the short fibers, unlike the long fibers, can exhibit merits in that it can give color-developing structures having excellent designability (decorativeness) in that the color tone varies depending on the angle of view.
Incidentally, polymer compounds employable for the fiber structures are exemplified by the following, as those for high-refractive index and low-refractive index, polymer compounds such as polyethylene, polybutylene, polyester, polyacrylonitrile, polystyrene, polyamide, polyolefin, polyvinyl alcohol, polycarbonate, methyl polymethacrylate, polyether ether ketone, polyparaphenylene terephthalamide and polyphenylene sulfide as single substances; blends of these compounds; or copolymers of two of more kinds. Further, low-refractive index polymer compounds can be exemplified by fluoroplastics, whereas high-refractive index polymer compounds can be exemplified by resins such as polyvinylidene chloride, polyethylene terephthalate and polyethylene naphthalate, and polyphenylene sulfide. Suitable combinations of low-refractive index polymer compounds and high-refractive index polymer compounds include combinations of the former compound selected from fluoroplastics and the latter compound selected from polyvinylidene chloride, polyester resins and polyphenylene sulfide.
Next, the length of the composite fiber will be described. FIG. 2 shows a composite short fiber for helping better understanding of the present invention, and this short fiber is formed by cutting a composite fiber.
In the color-developing composite short fiber according to the present invention, while the fiber is required to have a length in the range of 0.01 to 100 mm, the preferred range of length varies depending on the kind of structure to be formed employing the short fiber. For example, when the composite short fiber is used in the form of dispersion in or mixture with other materials such as coating material, the fiber conveniently has a length in the range of 0.01 to 2 mm. When the composite short fiber is used in the form of dispersion in or mixture with a coating material or the like, short fibers longer than the specified range will undergo torsion during dispersion to be liable to be bent, and color-development is hindered at such distorted portions, while color changes at the bent portions due to change in the structure. In the case of the short fiber having a length of 2 mm or shorter, even when the short fiber of the present invention is mixed with an adhesive and the resulting mixture is sprayed, clogging of spray nozzle does not occur, facilitating the operation. Meanwhile, in the case of the short fiber which is shorter than the specified range, it is technically difficult to cut a fiber material into fiber particles having a suitable size and suitable state in a large amount, leading to cost elevation. Consequently, the cut edges of the short fiber particles are deformed by the shear as shown in FIG. 2 to have no flat end which develop the original color of the fiber, and the color to be developed is changed.
On the other hand, when short fiber pieces are to be intertwined and bound to one another like in a nonwoven fabric, the short fiber suitably has a length of 2 to 30 mm.
Next, configuration and production techniques of a color-developing structure formed by adhering the short fiber of the present invention on the surface of a support such as a sheet and a metal plate, a color-developing structure such as a sheet formed using a binder resin in which the short fiber of the present invention is dispersed, a nonwoven fabric formed by intertwining the short fiber of the present invention, and a paper formed by dispersing in a paper raw material and bound therewith will be described below.
First, the color-developing structure formed by adhering the short fiber of the present invention on the surface of a support such as a sheet can be obtained by dispersing the short fiber by means of spraying or sprinkling utilizing the gravity and the like over the surface of the support which is coated on the surface with a material having adherence such as an uncured adhesive or coating to be adhered thereon, followed by curing of the uncured material. When the short fiber is to be applied over the entire surface of the support, a material having adherence may be applied over the entire surface of the support. However, for example, when a special pattern or the like is to be formed locally, an adhesive is applied patternwise beforehand, and the short fiber is dispersed on the surface of the adhesive layer thus formed, and after solidification of the adhesive, the short fiber present on the other portions of the support having no adhesive layer is removed to give the desired neat chromatic pattern.
The material of the support on which the short fiber is bonded may not particularly be limited, and various materials such as metals, wood, plastics, rubbers, ceramics, paper, fibers and glass can be employed, which may be employed not only singly but also as a mixture or laminate of two of more kinds. While the support may suitably be in the form of thin plate or thick plate, such as a film, a sheet or a plate, it may not necessarily be limited to plate-like bodies and may be of various kinds of three-dimensional structures. For example, patterns can be formed on toys using the short fiber, and articles whose designability and chromaticity are matters of great importance in daily lives can be decorated with the short fibers to make much of the characteristics of the short fibers. In the case of the structure employing the composite short fiber having the actions of reflecting both visible rays and invisible rays (e.g., infrared rays) and interfering therewith as set forth in the appended claim 2, the color-developing structure product obtained using as the support a fabric, a metal plate or the like can exhibit excellent chromaticity and also can inhibit temperature rise.
Meanwhile, if the color-developing structure is formed using as the plate-like support a transparent sheet 49 having a wavy surface as shown in FIG. 3, there is obtained a color-developing structure of excellent designability in that the orientation directions of the faces having optical properties are delicately changed following the wave to vary the color tone to be developed delicately. Otherwise, the wavy surface may be oriented not to be exposed but to be the rear side, and thus the surface of the structure can securely be prevented from being soiled or damaged. It is also possible to control securely damage, soiling, etc. of the structure by applying a transparent sheet layer or forming a transparent coating layer on the surface of the support on which the color-developing short fiber is adhered as shown in FIGS. 4(b) and 4(C). In the case of the former, since the surface of the structure can be flattened, it can be desoiled easily by wiping. The resulting sheet-like color-developing structure can be applied easily to various kinds of articles if an adhesive layer is formed on the rear side of the structure to readily exhibit fully its optical properties.
Further, this short fiber can be used in combination with other surface decorating materials such as coating materials. In such a case, the short fiber may first be bonded to a support, followed by coating of the resulting support with a coating material. Otherwise, a coating material may first be applied to the support, followed by dispersion of the short fiber before the coating material is dried to bind the short fiber onto the support with the aid of the adhesion of the coating material. Further, the short fiber may be used in the form of mixture with an adhesive or a coating material, and the resulting mixture can be sprayed. As the coating material to be employed here, those which do not affect color-developing properties of the short fiber are preferably selected. Particularly, when orientation of the color-developing surface characteristic to the short fibers is not very important, mixing of the short fibers with coating materials presents no problem, and further the short fiber can be used in the form of mixture with various kinds of materials which are required to develop color.
Next, nonwoven fabric consisting only of color-developing composite fiber particles which are bound to one another, paper obtained by dispersing the short fiber particles in and bound with other paper materials, and the like can be prepared in the following manner.
A composite fiber filament is first cut into particles of several millimeters, and the fiber particles are dispersed homogeneously in a paper-making raw material mixture containing water, a dispersant, a precipitant and a glue. Subsequently, the resulting dispersion is applied to the same paper-making equipment having at the bottom a fine mesh as used in ordinary paper making to prepare a wet paper sheet, followed by drying to give a paper sheet as a final product containing the color-developing composite short fiber dispersed therein. Meanwhile, after the composite fiber filament is cut into particles of several millimeters, the fiber particles are dispersed homogeneously in a binder resin solution, and the resulting dispersion is made into the form of sheet or film. If an adhesive layer is formed on one side of the sheet obtained, it can be applied to various kinds of articles easily.